Commit-ID: fb6a44f33be542fd81575ff93a4e8118d6a58592
Gitweb: http://git.kernel.org/tip/fb6a44f33be542fd81575ff93a4e8118d6a58592
Author: Waiman Long <Waiman.Long@xxxxxxx>
AuthorDate: Tue, 17 May 2016 21:26:20 -0400
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 8 Jun 2016 15:16:59 +0200
locking/rwsem: Protect all writes to owner by WRITE_ONCE()
Without using WRITE_ONCE(), the compiler can potentially break a
write into multiple smaller ones (store tearing). So a read from the
same data by another task concurrently may return a partial result.
This can result in a kernel crash if the data is a memory address
that is being dereferenced.
This patch changes all write to rwsem->owner to use WRITE_ONCE()
to make sure that store tearing will not happen. READ_ONCE() may
not be needed for rwsem->owner as long as the value is only used for
comparison and not dereferencing.
Signed-off-by: Waiman Long <Waiman.Long@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Douglas Hatch <doug.hatch@xxxxxxx>
Cc: Jason Low <jason.low2@xxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Scott J Norton <scott.norton@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1463534783-38814-3-git-send-email-Waiman.Long@xxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/locking/rwsem.h | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/kernel/locking/rwsem.h b/kernel/locking/rwsem.h
index 8f43ba2..a699f40 100644
--- a/kernel/locking/rwsem.h
+++ b/kernel/locking/rwsem.h
@@ -16,14 +16,21 @@
#define RWSEM_READER_OWNED ((struct task_struct *)1UL)
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
+/*
+ * All writes to owner are protected by WRITE_ONCE() to make sure that
+ * store tearing can't happen as optimistic spinners may read and use
+ * the owner value concurrently without lock. Read from owner, however,
+ * may not need READ_ONCE() as long as the pointer value is only used
+ * for comparison and isn't being dereferenced.
+ */
static inline void rwsem_set_owner(struct rw_semaphore *sem)
{
- sem->owner = current;
+ WRITE_ONCE(sem->owner, current);
}
static inline void rwsem_clear_owner(struct rw_semaphore *sem)
{
- sem->owner = NULL;
+ WRITE_ONCE(sem->owner, NULL);
}
static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
@@ -34,7 +41,7 @@ static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
* to minimize cacheline contention.
*/
if (sem->owner != RWSEM_READER_OWNED)
- sem->owner = RWSEM_READER_OWNED;
+ WRITE_ONCE(sem->owner, RWSEM_READER_OWNED);
}
static inline bool rwsem_owner_is_writer(struct task_struct *owner)
--
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